Android 输入框限制字符输入数

有时候对Android的输入框有字符输入数量的限制，并且显示显示字符输入的数量。通过以下方式可以实现：

1.子定义LimitNumEditText继承EditText

import android.content.Context;
import android.content.res.TypedArray;
import android.telephony.SmsMessage;
import android.text.Editable;
import android.text.InputFilter;
import android.text.TextWatcher;
import android.util.AttributeSet;
import android.widget.EditText;

import us.pinguo.cc.R;

/**
 * Created by crab on 15-3-18.
 */
public class LimitNumEditText extends EditText {
    private int mMaxLength;
    private OnTextCountChangeListener mTextCountChangeListener;

    public LimitNumEditText(Context context) {
        this(context, null);
    }

    public LimitNumEditText(Context context, AttributeSet attrs) {
        super(context, attrs);
        TypedArray typedArray = context.obtainStyledAttributes(attrs, R.styleable.LimitNumEditText);
        mMaxLength = typedArray.getInt(R.styleable.LimitNumEditText_maxLength, -1);
        typedArray.recycle();
        if (mMaxLength >= 0) {
            setFilters(new InputFilter[]{new InputFilter.LengthFilter(mMaxLength)});
        } else {
            setFilters(new InputFilter[0]);
        }
        addTextChangedListener(null);
    }
    /**
     * @return 返回限制输入的最大字符数量
     */
    public int getLimitLength(){
        return mMaxLength;
    }
    @Override
    public void addTextChangedListener(final TextWatcher watcher) {
        TextWatcher inner=new TextWatcher() {
            @Override
            public void beforeTextChanged(CharSequence s, int start, int count, int after) {
                if(watcher!=null){
                    watcher.beforeTextChanged(s,start,count,after);
                }
            }

            @Override
            public void onTextChanged(CharSequence s, int start, int before, int count) {
                int[] params= SmsMessage.calculateLength(s,false);
                int use=params[1];
                if(mMaxLength>=0 && mTextCountChangeListener!=null){
                    mTextCountChangeListener.onTextCountChange(use,mMaxLength);
                }
                if(watcher!=null){
                    watcher.onTextChanged(s,start,before,count);
                }
            }

            @Override
            public void afterTextChanged(Editable s) {
                if(watcher!=null){
                    watcher.afterTextChanged(s);
                }
            }
        };
        super.addTextChangedListener(inner);
    }

    public LimitNumEditText(Context context, AttributeSet attrs, int defStyle) {
        super(context, attrs, defStyle);
    }
    public void setOnTextCountChangeListener(OnTextCountChangeListener listener){
        mTextCountChangeListener=listener;
    }
    /**
     * 监听输入框字符变化
     */
    public interface OnTextCountChangeListener{
        /**
         *
         * @param use 输入字符赞据的大小
         * @param total 限制输入数量的上线
         */
        public void onTextCountChange(int use, int total);
    }

2.修改res/values/attrs.xml文件，增加如下行

<declare-styleable name="LimitNumEditText">

<attr name="maxLength" format="integer" />

</declare-styleable>

3.在布局文件中使用

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:algnText="http://schemas.android.com/apk/res-auto"
    android:background="#FFFFFF"
    android:orientation="vertical"
    android:layout_width="match_parent"
    android:layout_height="match_parent">
    <com.example.crab.mycameratest.LimitNumEditText
        algnText:maxLength="20"
        android:id="@+id/id_edit_text_test"
        android:layout_width="match_parent"
        android:layout_height="50dp"/>
</LinearLayout>